Method of manufacturing heat exchanger

Abstract

In the method of manufacturing a heat exchanger, transverse sectional shapes of heat exchanging tubes can be easily formed into elliptical shapes. The method includes the steps of: piling metallic fins, each of which includes collared through-holes, so as to form tube holes, which are formed by connecting the collared through-holes; piercing heat exchanging tubes, whose transverse sectional shapes are circular shapes, through the tube holes; and inserting expanding bullets, whose transverse sectional shapes are elliptical shapes, into the heat exchanging tubes. The heat exchanging tubes are elliptically expanded to and integrated with the metallic fins.

What is claimed is:  
     
       1. A method of manufacturing a heat exchanger, comprising the steps of: 
       piling a plurality of metallic fins, each of which includes a plurality of circular collared through-holes, so as to form a plurality of tube holes, each of which is formed by connecting said circular collared through-holes;  
       piercing heat exchanging tubes, whose transverse sectional shapes are circular shapes, through said tube holes, wherein orienting said transverse sectional shapes of said heat exchanging tubes relative to transverse sections of said collared through-holes is avoided;  
       inserting expanding bullets, whose transverse sectional shapes are elliptical shapes which are gradually reduced toward a bottom side, into said heat exchanging tubes,  
       thereby expanding said heat exchanging tubes,  
       transforming their transverse sections from circular shapes to elliptical shapes, and  
       integrating said heat exchanging tubes with said metallic fins.  
     
     
       2. The method according to  claim 1 , 
       wherein an outer major axis of each of said heat exchanging tubes expanded is greater than an inner diameter of each of said collared through-holes not expanded, and  
       an outer minor axis of each of said heat exchanging tubes expanded is equal to the inner diameter of each of said collared through-holes not expanded.  
     
     
       3. The method according to  claim 2 , 
       wherein deformation absorbing sections, which are capable of absorbing deformation of said metallic fin, which occurs in the vicinity of said collared through-holes when said heat exchanging tubes are expanded, are formed in each of said metallic fins.  
     
     
       4. The method according to  claim 3 , 
       wherein said deformation absorbing sections are circular projections, which respectively enclose said collared through-holes and which are formed by bending said metallic fin.  
     
     
       5. A method of manufacturing a heat exchanger comprising the steps of: 
       piling a plurality of metallic fins, each of which includes a plurality of circular collared through-holes surrounded by circular deformation absorbing sections having projections capable of absorbing deformation of said metallic fins, which occurs in the vicinity of said circular collared through-holes, the piling forming a plurality of tube holes, each of which is formed by connecting said circular collared through-holes;  
       piercing heat exchanging tubes, whose transverse sectional shapes are circular shapes, through said tube holes, wherein orienting transverse sectional shapes of said heat exchanging tubes relative to transverse cross sections of said collared through-holes is avoided;  
       inserting expanding bullets, whose transverse sectional shapes are elliptical shapes which are gradually reduced toward a bottom side, into said heat exchanging tubes,  
       thereby expanding said heat exchanging tubes,  
       transforming their transverse sections from circular shapes to elliptical shapes, whose outer major axes are greater than inner diameters of said collared through-holes not expanded and whose outer minor axes are equal to the inner diameters thereof, in transverse sections,  
       causing said deformation absorbing sections to absorb the deformation resulting from the expanding tubes, and  
       integrating said heat exchanging tubes with said metallic fins.  
     
     
       6. A method of manufacturing a heat exchanger, comprising the steps of: 
       piling a plurality of metallic fins, each of which includes a plurality of collared through-holes, so as to form a plurality of tube holes, each of which is formed by connecting said collared through-holes;  
       piercing heat exchanging tubes, whose transverse sectional shapes are circular shapes, through said tube holes, wherein orienting said transverse sectional shapes of said heat exchanging tubes relative to transverse sections of said collared through-holes is avoided;  
       inserting expanding bullets, whose transverse sectional shapes are elliptical shapes which are gradually reduced toward a bottom side, into said heat exchanging tubes,  
       thereby expanding said heat exchanging tubes,  
       transforming their transverse sections from circular shapes to elliptical shapes, and  
       integrating said heat exchanging tubes with said metallic fins.